In the field of medicine, there is a growing recognition that it is important that the joint of a person especially those of the spine, be in proper position for better mental and physical health. Indeed, the recognized and growing medical field of chiropractic involves methods for treating various ailments by adjustments of the joints, especially the spinal vertebrae, (subluxations).
It will be appreciated that, because there are many practitioners in the field of chiropractic, there are also many different variations in the actual performance of any given common recognized chiropractic technique. For example, the degree of force and direction of force applied to a patient in performing a recognized adjustment technique often varies from one practitioner to another practitioner due to human error, variances in size and strength and other variables which, inevitably yields in variable results. Accordingly, there has long been an appreciation of the fact that it would be generally beneficial to practitioners and patients alike if a successful adjustment technique could be reproduced by a broad spectrum of practitioners in a more uniform and consistent manner to provide more predictable and reproducible results.
It has been discovered that an instrument designed to deliver an impact to the spinal vertebrae is useful in attempting to achieve more consistent results of spinal adjustments. Thus, impact or mallet type instruments have been used in the chiropractic field. Specifically, there have been impact or mallet type instruments in the past which include a housing, a piston with an exposed impact head and an opposite end captivated in the housing, spring means in the housing engaging the piston and normally urging it to an extended normal position so that the piston can be forced axially to a retracted position, compressing the spring to a predetermined position and thereafter releasing the piston to the extended position. A representative mallet instrument of this type is disclosed in U.S. Pat. No. 2,421,354 to Reiter, directed to a surgical mallet instrument. Instruments of the same mechanical structure as the Reiter instrument, as well as modified instruments, have been used in the chiropractic field to perform adjustments of the spinal vertebrae. The piston and impact heads of these instruments releases automatically when the piston is pulled back against the spring to a predetermined position, at which point the piston and impact head are released outwardly to deliver a straight axial impact force. Thus, these instruments do not provide any means for "cocking" the piston or a trigger mechanism activated by external pressure to the distal tip of the piston for releasing the cocked piston. The amount of force delivered by the impact head cannot be adjusted, as the spring is compressed to the same level each time the piston reaches the predetermined release position. Further, the distal tip of the piston of these instruments is not structured for removable attachment of various impact heads of different sizes, shapes and densities, nor are they structured for selective clockwise or counterclockwise rotation of the distal tip to provide a torsional impact force.